The ability of the Vigileo-FloTrac system to measure cardiac output and track cardiac output changes during one-lung ventilation

Effects of phenylephrine on systemic and cerebral circulations in humans: a systematic review with mechanistic explanations

We conducted a systematic review of the literature reporting phenylephrine-induced changes in blood pressure, cardiac output, cerebral blood flow and cerebral tissue oxygen saturation as measured by near-infrared spectroscopy in humans. We used the proportion change of the group mean values reported by the original studies in our analysis. Phenylephrine elevates blood pressure whilst concurrently inducing a reduction in cardiac output. Furthermore, despite increasing cerebral blood flow, it decreases cerebral tissue oxygen saturation. The extent of phenylephrine's influence on cardiac output (r = -0.54 and p = 0.09 in awake humans; r = -0.55 and p = 0.007 in anaesthetised humans), cerebral blood flow (r = 0.65 and p = 0.002 in awake humans; r = 0.80 and p = 0.003 in anaesthetised humans) and cerebral tissue oxygen saturation (r = -0.72 and p = 0.03 in awake humans; r = -0.24 and p = 0.48 in anaesthetised humans) appears closely linked to the magnitude of phenylephrine-induced blood pressure changes. When comparing the effects of phenylephrine in awake and anaesthetised humans, we found no evidence of a significant difference in cardiac output, cerebral blood flow or cerebral tissue oxygen saturation. There was also no evidence of a significant difference in effect on systemic and cerebral circulations whether phenylephrine was given by bolus or infusion. We explore the underlying mechanisms driving the phenylephrine-induced cardiac output reduction, cerebral blood flow increase and cerebral tissue oxygen saturation decrease. Individualised treatment approaches, close monitoring and consideration of potential risks and benefits remain vital to the safe and effective use of phenylephrine in acute care.

Validation of cardiac output estimation using the fourth-generation FloTrac/EV1000™ system in patients undergoing robotic-assisted off-pump coronary artery bypass surgery

The pulmonary artery catheter (PAC)-despite its invasiveness-remains the gold standard for cardiac output (CO) monitoring. The FloTrac system, a less invasive hemodynamic monitor has been developed, which estimates CO using arterial pressure waveform analysis without external calibration. Recently, an upgraded version of FloTrac system with improved algorithm to follow changes in vascular resistance was introduced into the market. The aim of this study was to assess the reliability of the CO estimated from the fourth-generation FloTrac/EV1000 system (CO_FT) compared to that measured with PAC using the thermodilution method (CO_PAC) during robotic-assisted off-pump coronary artery bypass (OPCAB) surgery. CO_FT and CO_PAC were obtained simultaneously at 4 predefined time points during robotic-assisted OPCAB: 5 min after the induction of general anesthesia (T1), after starting one-lung ventilation (T2), after capnothorax (T3), and after mini-thoracotomy was performed (T4). The agreement of data was investigated by Bland-Altman analysis. Thirty-four patients were initially enrolled. After exclusion, 32 patients and a total of 128 paired CO measurements were obtained. The overall bias was 1.46 L/min, the 95% limits of agreements were - 3.40 to 6.33 L/min, and the percentage error was 72.98%. Regression analysis of the systemic vascular resistance index (SVRI) and the bias between CO_PAC and CO_FT showed that the bias was moderately correlated with the SVRI (r² = 0.43; p < 0.0001). Despite a software upgrade, the reliability of the fourth-generation FloTrac/EV1000™ system during robotic-assisted OPCAB to estimate CO was not acceptable, especially in patients with low SVRI.

Hypoxemia During One-Lung Ventilation: Does It Really Matter?

PURPOSE OF REVIEW

Hypoxemia during one-lung ventilation, while decreasing in frequency, persists as an intraoperative challenge for anesthesiologists. Discerning when desaturation and resultant hypoxemia correlates to tissue hypoxia is challenging in the perioperative setting and requires a thorough understanding of the physiology of oxygen delivery and tissue utilization.

RECENT FINDINGS

Oxygen delivery is not directly correlated with peripheral oxygen saturation in patients undergoing one-lung ventilation, emphasizing the importance of hemoglobin concentration and cardiac output in avoiding tissue hypoxia. While healthy humans can tolerate acute hypoxemia without long-term consequences, there is a paucity of evidence from patients undergoing thoracic surgery. Increasingly recognized is the potential harm of hyperoxic states, particularly in the setting of complex patients with comorbid diseases.

SUMMARY

Anesthesiologists are left to determine an acceptable oxygen saturation nadir that is individualized to the patient and procedure based on an understanding of oxygen supply, demand, and the consequences of interventions.

Effect of Systemic Vascular Resistance on the Reliability of Noninvasive Hemodynamic Monitoring in Cardiac Surgery

OBJECTIVE

To assess the effect of systemic vascular resistance (SVR) on the reliability of the ClearSight system (Edwards Lifesciences, Irvine, CA) for measuring blood pressure (BP) and cardiac output (CO).

DESIGN

Observational study.

SETTING

University hospital.

PARTICIPANTS

Twenty-five patients undergoing cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

BP, measured using ClearSight and an arterial line, and CO, measured using ClearSight and a pulmonary artery catheter, were recorded before (T1) and two minutes after phenylephrine or ephedrine administration. Bland-Altman analysis was used to compare BP and CO measurements at T1. A polar plot was used to assess trending abilities. Patients were divided into the following three groups according to the SVR index (SVRI) at T1: low (<1,200 dyne s/cm⁵/m²), normal (1,200-25,00 dyne s/cm⁵/m²), and high (>2,500 dyne s/cm⁵/m²). The bias in BP and CO was -4.8 ± 8.9 mmHg and 0.10 ± 0.81 L/min, respectively, which was correlated significantly with SVRI (p < 0.05). The percentage error in CO was 40.6%, which was lower in the normal SVRI group (33.3%) than the low and high groups (46.3% and 47.7%, respectively). The angular concordance rate was 96.3% and 95.4% for BP and 87.0% and 92.5% for CO after phenylephrine and ephedrine administration, respectively. There was a low tracking ability for CO changes after phenylephrine administration in the low-SVRI group (angular concordance rate 33.3%).

CONCLUSION

The ClearSight system showed an acceptable accuracy in measuring BP and tracking BP changes in various SVR states; however, the accuracy of CO measurement and its trending ability in various SVR states was poor.

Impact of non-invasive continuous blood pressure monitoring on maternal hypotension during cesarean delivery: a randomized-controlled study

PURPOSE

This study aimed to investigate the efficacy of the ClearSight™ system (Edwards Lifesciences, Irvine, CA) for reducing the incidence of hypotension compared with the traditional oscillometric blood pressure monitoring in cesarean delivery under spinal anesthesia.

METHODS

Forty patients undergoing cesarean delivery under spinal anesthesia were enrolled. The patients were randomly divided into two groups (Control and ClearSight groups). All patients received spinal anesthesia using 0.5% hyperbaric bupivacaine (11.5 mg) and fentanyl (10 µg). Blood pressure was managed with the same protocol using the ClearSight™ system (ClearSight group) and oscillometric blood pressure monitoring (Control group). Furthermore, we compared the accuracy of the ClearSight™ system with the traditional oscillometric monitoring for blood pressure measurement using Bland-Altman, four-quadrant plot, and polar plot analyses.

RESULTS

The incidence of hypotension was significantly lower in the ClearSight group from induction to delivery (45% vs. 0%, p < 0.001) and to the end of surgery (50% vs. 20%, p = 0.049). Intraoperative nausea occurred more frequently in the Control group (45% vs. 10%, p = 0.012). The ClearSight™ system demonstrated acceptable accuracy with a bias of - 4.3 ± 11.7 mmHg throughout the procedure. Four-quadrant analysis revealed an excellent trending ability of the ClearSight™ system with a concordance rate of approximately 95%. In the polar plot analysis, the angular bias and concordance rate were - 13.5° ± 19.0° and 76.9%, respectively.

CONCLUSIONS

The accuracy and trending ability of the ClearSight™ system for blood pressure measurement was clinically acceptable in cesarean delivery under spinal anesthesia, leading to reductions in maternal hypotension and nausea.

Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery

BACKGROUND

Spinal anaesthesia carries a risk of hypotension. We hypothesized that pleth variability index and perfusion index would assess maternal volume status, and thus, allow identification of patients at higher risk of developing hypotension after spinal anaesthesia for caesarean delivery.

METHODS

Fifty patients undergoing elective caesarean delivery were enrolled. All patients received spinal anaesthesia with 0.5% hyperbaric bupivacaine (10 mg) and fentanyl (10 mcg). Blood pressure was measured every minute. Pleth variability index and perfusion index were automatically measured throughout the procedure using pulse oximetry on the index finger. In case of hypotension (systolic blood pressure below 90 mmHg or 80% of the baseline value), ephedrine 5 mg was administered. Receiver-operating characteristic and multivariate logistic regression analyses for spinal anaesthesia-induced hypotension were performed.

RESULTS

Hypotension occurred in 32 patients (64%). The areas under the receiver-operating characteristic curve were 0.751 (95% confidence interval: 0.597-0.904) for pleth variability index before anaesthesia, 0.793 (95% confidence interval: 0.655-0.930) for pleth variability index after anaesthesia and 0.731 (95% confidence interval: 0.570-0.892) for perfusion index change (percent change in perfusion index induced by spinal anaesthesia). The optimal threshold value of pleth variability index (after anaesthesia) for predicting hypotension was 18% (sensitivity: 78.1%, specificity: 83.3%). Pleth variability index after spinal anaesthesia was an independent factor for hypotension (odds ratio: 1.21, P = 0.041).

CONCLUSIONS

Pleth variability index after spinal anaesthesia was a good predictor of spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery. In addition, perfusion index change after spinal anaesthesia has the potential to predict hypotension.

Electrical velocimetry for noninvasive cardiac output and stroke volume variation measurements in dogs undergoing cardiovascular surgery

OBJECTIVE

To compare electrical velocimetry (EV) noninvasive measures of cardiac output (CO) and stroke volume variation (SVV) in dogs undergoing cardiovascular surgery with those obtained with the conventional thermodilution technique using a pulmonary artery catheter.

STUDY DESIGN

Prospective experimental trial.

ANIMALS

Seven adult Beagle dogs with a median weight of 13.6 kg.

METHODS

Simultaneous, coupled cardiac index (CI; CO indexed to body surface area) measurements by EV (CI_EV) and the reference pulmonary artery catheter thermodilution method (CI_PAC) were obtained in seven sevoflurane-anaesthetized, mechanically ventilated dogs undergoing experimental open-chest cardiovascular surgery for isolated right ventricular failure. Relationships between SVV or central venous pressure (CVP) and stroke volume (SV) were analysed to estimate fluid responsiveness. Haemodynamic data were recorded intraoperatively and before and after fluid challenge.

RESULTS

Bland-Altman analysis of 332 matched sets of CI data revealed an overall bias and precision of - 0.22 ± 0.52 L minute^-1 m^-2 for CI_EV and CI_PAC (percentage error: 30.4%). Trend analysis showed a concordance of 88% for CI_EV. SVV showed a significant positive correlation (r² = 0.442, p < 0.0001) with SV changes to a volume loading of 200 mL, but CVP did not (r² = 0.0002, p = 0.94). Better prediction of SV responsiveness (rise of SV index of ≥ 10%) was observed for SVV (0.74 ± 0.09; p = 0.014) with a significant area under the receiver operating characteristic curve in comparison with CVP (0.53 ± 0.98; p = 0.78), with a cut-off value of 14.5% (60% specificity and 83% sensitivity).

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs undergoing cardiovascular surgery, EV provided accurate CO measurements compared with CI_PAC, although its trending ability was poor. Further, SVV by EV, but not CVP, reliably predicted fluid responsiveness during mechanical ventilation in dogs.